The present invention relates to an optoelectronic sensor.
In the case of optodes used in fire alarm systems, there are various different ways to implement optical measuring systems. One approach is Multiple Internal Reflection/Attenuated Total Reflection (MIRE/ATR), which involves injecting light into a highly refractive material so that the light undergoes total reflection, a membrane having been deposited on the highly refractive material so that the evanescent field of the light that has been injected is absorbed by the membrane. If the membrane comes into contact with an analytexe2x80x94a gas to be measuredxe2x80x94the membrane""absorption and thus absorption of the light changes. Thus by measuring the absorption it is possible to measure the concentration of the gas to be measured, because the membrane changes its absorption characteristics based on the concentration of the gas. Herein, one necessary condition is that only the evanescent field penetrates into the membrane and is absorbed.
Another measuring method is transmission measurement. In this case too, changes in absorption are measured. Herein, light passes through a membrane that comes into contact with the analyte, absorption by the membrane changing as a function of the analyte. By carrying out comparison measurements with and without the analyte, it is possible to determine the analyte. If necessary a rinsing solution can be used to remove the analyte from the membrane between measurements.
By contrast, the optoelectronic sensor according to the present invention has the advantage that the light does not have to be injected into the optode causing total reflection, so that the light can be injected into the optode at any angle desired, as the optode has a mirror that reflects the light on the edge of the optode back into the optode. As a result, greater angles can be used for injecting the light, so that the optical path through the optode from the light emitter to the light-sensitive sensors is longer than if only the angles for total reflection were used. Thus the measuring sensitivity is greater, as the interaction of the light with the optode is possible over a longer path. The measurement regarding the gas, which is to be analyzed and which penetrates the optode, can be determined immediately via the light-sensitive sensors.
This increased measuring sensitivity can be used advantageously to simply and quickly spot the early stages of jaundice in babies, the carbon monoxide content of the baby""s exhaled breath being analyzed. If the carbon monoxide content exceeds 1.8 ppm, this indicates that the baby may possibly have jaundice. The optoelectronic transmitter according to the present invention supplies a measurement immediately, so that timely, life-saving treatment can be provided.
It is especially advantageous that the mirror is created on the outside of the optode material via metallic particles that are introduced. This method is straightforward and can easily be integrated into the production process for the optoelectronic sensor.
Furthermore it is advantageous that covering the optode material with an opaque material keeps light from exiting via scattered light. This reduces the effect of scattered light on the measurement being carried out, and thus increases the precision of the measurement.
Furthermore, it is advantageous that the optode material is a polymer to which an indicator substance is added. Using a polymer along with an indicator substance makes it easier to produce the optode material and apply it to the semiconductor substrate.
Furthermore, it is advantageous that pigment molecules are present in the indicator substance and result in gas-dependent absorption of the light that is injected. It is advantageous that these pigment molecules allow reversible, gas-type-dependent absorption, which is then used to determine the gas concentration via the absorption that is measured.
Furthermore, it is advantageous that the opaque material is embodied as a polymer, which means the production process for this opaque layer can be tailored to the production process for the optodes. Thus the production process as a whole can be simplified.
Furthermore, it is advantageous that the light-sensitive sensors having the sections of the optode material that cover them are arranged as sectors and rotationally symmetrically around the light emitter. Thus the light emitted by the light emitter is distributed evenly and used to carry out measurement in the various sections that are covered by the optode material.
A chip that forms the optoelectronic sensor can thus be embodied as square, as having 5, 6, 7, or 8 corners, or as circular. In addition, an optoelectronic sensor of this kind may also include fewer than or more than four transmission branches.
Furthermore, it is advantageous that the semiconductor substrate is formed from n-type silicon, and the light-sensitive elements are formed from p-type silicon areas that are integrated into the n-type silicon substrate. In this way the light-sensitive elements form photodiodes. The light emitter is preferably anxe2x80x94LED; it is also possible to provide a plurality of LEDs to define the wavelength.
Furthermore, it is advantageous that the optode material is designed to detect nitrogen oxides, so that these gases that characterize a fire can be detected quantitatively by the fire alarm having the optoelectronic sensor. Thus, on the basis of the high degree of measuring sensitivity of the optoelectronic sensor according to the present invention, fires can be detected early.
Furthermore, it is advantageous that the sensor according to the present invention has an oxidation material provided on a carrier material to keep the sensor according to the present invention from being damaged by sulfur dioxide. Alternatively, it is possible for the sensor according to the present invention to have a molecular sieve that filters out undesired gases.
In the optoelectronic sensor the individual transmission branches are separated by barriers so that the individual transmission branches do not influence each other optically due to scattered light exiting from the optode material. The height of these barriers may be roughly equal to the height of the central light sensor. In addition, all parts of the chip that are not light sensitive may, if necessary, be rendered reflective, this including the sidewalls of the barriers. To accomplish this, it is advantageous to carry out metallization, preferably using gold.
Furthermore, it is advantageous that the light emitter is operated using pulses, so that the power consumption of the sensor according to the present invention is reduced.
By combining a plurality of optoelectronic sensors to form a sensor array, a high degree of measuring precision can be achieved, and large attack surfaces for the gas to be detected can be provided. To accomplish this, the optoelectronic sensor according to the present invention has conductors, some of which supply power to the light emitter and the light sensitive sensors, while others pick off the measurement signals.